From dogs that sniff each other's butts to cats that spray to mark their territory, waste products seem to take on a special meaning in the animal kingdom. A new study has erm, dug deeper into this phenomenon, examining the compounds steaming from rhino dung and finding that they serve as information centers to determine things like the sex, fertility, and territorial ambitions of the recently relieved.
That mammals use the olfactory signals in urine to communicate is well known, with the need to mark territory, send a warning signal to intruders or attract prey all perfectly valid reasons to stop, prop and take a whiz (or a whiff). Dung too is known to play some sort of role, with earlier behavioral studies suggesting that animals can draw information from excrement, including fertility in cows and horses.
But a team of researchers from South Africa's University of KwaZulu-Natal set out to build on this knowledge in a few ways. They wanted to explore the role of excremental communication in wild animals, which they say have gone understudied, by discovering the precise VOCs, or volatile organic compounds, responsible for passing on messages. The importance of communal defecation sites, known as middens, were also of interest.
So the researchers ventured out into South Africa's Hluhluwe-iMfolozi Park and scooped up 150 dung samples left by individual free-ranging white rhinos and categorized them into different age groups, sexes, and fertility and territorial profiles. They then studied the odors emitted from the waste to quantify the VOCs using gas chromatography-mass spectrometry, an instrumental technique used to analyze low molecular weight compounds in environmental materials.
The team found that a certain compound, called 2,3-dimethylundecane, appeared to be indicative of an individual rhino's sex, age class and territorial status, while another called 2,6-dimethylundecane indicated female fertility. To further explore the significance of these signals, the team actually reproduced artificial dung odor profiles, laid them out in the middens and set up camera traps to see how territorial male rhinos responded.
It found that the wild rhinos behaved in the ways it expected. A sign of another territorial male? The rhinos both increased the frequency of its visits to the midden and more quickly assumed a "vigilance posture." A whiff of a female on heat? The rhinos upped their visits to the midden and spent significantly more time sniffing around.
Because white rhinos of all ages do their business in these communal sites, the researchers conclude that the middens probably act as "information centers." Furthermore, because other mammals practice the same ritual, they write that it is likely that these kinds of communication hubs are a "widespread phenomenon."
The research was published in the Proceedings of the Royal Society B.